Ultrasonic imaging is widely used in the medical field because its non-ionizing radiation present a low risk to the patient being treated. The ultrasonic devices that have been developed employ sound frequencies in the 1 to 20 MHz range. Pulses within this range are propagated through the body of a patient and a small portion of the energy is reflected back to provide an image of the tissue upon which the sound waves have impinged with the brightness of reflected signal being a measure of tissue density. Doppler shifting of the returning sound can also be used to determine the flow velocity of moving structures such as blood moving through a vessel or an organ.
Ultrasonic instruments are widely-used to study the functioning of an unborn fetus as well as diagnosing disorders that might be present within the fetus. One such disorder is a malfunction of the aortic valve. If not timely treated while the fetus is into womb, the baby will invariable not be alive at birth. The accepted practice for treating this type of malfunction is to insert a balloon catheter into the troubled area and inflating and deflating the balloon to assist the heart and the aortic valve in establishing a rhythmic beat.
The balloon is positioned within the aorta using a needle that includes a thin walled tubular body and an obturator that is removably contained within the body section. The needle is passed into the fetus through the abdominal wall of the mother and then into the aorta. Once the needle is generally positioned, the obturator is removed and a balloon, which is attached to the distal end of a catheter is passed through the needle and is more accurately located within the aorta. Here again, ultrasonic imaging is employed to position the needle and thus locate the balloon within the aorta in order to protect both the mother and the baby from harm during the procedure.
Although ultrasonics at the 1-10 MHz range provides a relatively good image of human tissue, the return from metal objects is considerably less than satisfactory. Accordingly, accurate positioning of a metal needle within a fetus is difficult to arrive at and sometimes involves a good deal of guess work on the part of the attending physician. It is also sometimes rather difficult to withdraw the catheter through the needle at the end of the procedure because the deflated balloon can become snagged by the tip of the thin walled needle as the deflated balloon re-enters the body section. In some cases the balloon can be stripped from the catheter worsening the re-entry problem.